Chemical and pharmaceutical processing plants use smart devices to monitor pressure during process operations. Smart devices are precisely calibrated with a pressure controller/calibrator before they are installed in a manufacturing process. Smart devices for sensing pressure have two key items to be calibrated. The first and foremost item is calibrating the pressure-to-resistance (or pressure-to-voltage) relationship of the transducer, and the second item is calibrating the linearity and offset of the conversion of electrical signal from the transducer into a 4-20 milliamp signal. Calibrating the transducer requires a pressure source such as a reference pressure source or a handheld pump and a precision pressure controller/calibrator.
A smart device has one or more transducers that measure physical parameters, such as pressure or temperature or whether a valve is open or closed. Transducers convert a signal of parameters in one form of energy (e.g., pressure, flow) into electrical signals. The output of the transducer is converted from analog to digital values by an analog-to-digital converter whose output is input to a microprocessor. Some smart devices may have a microprocessor and circuitry for performing A-to-D and D-to-A conversion in a single chip. Depending upon the type of communication network, after processing, the microprocessor output may be converted into an analog value for transmission via a wired or wireless transmitter.
If the transducer is out of tolerance, the span and offset may have to be adjusted on the smart device. If the transmitter uses a digital communication protocol the span and offset is adjusted through a digital communicator or with a documenting process calibrator capable of digital communication. Otherwise, trim pots on the transmitter are used to adjust the span and offset. The need to achieve consistent results is one of the most important reasons for calibration.
Process plants may have hundreds of pressure measuring stations with each station having a pressure transducer/transmitter to sense pressure at the station and communication channels to send the pressure data to a central monitor. Field calibration equipment may calibrate the smart devices while they are in use. However, smart devices wear, become damaged and fail. When that occurs they must be taken out of service, repaired or replaced, and calibrated with a laboratory calibrator also known as a pressure controller/calibrator. New and repaired smart devices undergo a highly precise calibration procedure using a laboratory pressure controller/calibrator. Because of the large number of smart devices requiring laboratory calibration, it is desired to provide a pressure controller/calibrator that can easily connect and disconnect the smart devices under test (DUT) to precise pressure standards for performing calibration operations on the DUTs.
Current pressure controller/calibrators have one or more pressure standard stations in the controller. Each pressure standard station has a highly precise pressure transducer. The laboratory calibrator compares readings of a pressure source sensed by the highly precise pressure transducer and the transducer of the smart device. However, each pressure standard station has a limited range, e.g., 0-100 psi, 200-300 psi, 500-1,000 psi, etc. A pressure controller/calibrator may have one or two pressure standard stations in the pressure controller. However, each pressure standard can only calibrate a limited pressure range. Real world processing operations have a large range of operating pressures but pressure standard stations have limited ranges. In order to accommodate the variety of pressure ranges, process operators may need a large number of pressure controller/calibrators, each having one or two pressure standard stations dedicated to one or two predetermined ranges. As such multiple pressure controllers are needed to calibrate the variety of smart devices that span the large number of pressure ranges.
Others have proposed modular pressure standard stations for pressure controllers/calibrators with the goal of swapping pressure standards with different pressure ranges into and out of a common pressure controller. However, such known modular pressure stations require an operator to substantially disassemble the pressure controller in order to interchange modular pressure stations. More specifically, a user has to individually connect and individually disconnect each pneumatic and electrical connection between the modular pressure station and the chassis of the pressure controller. If the module is not properly aligned, the fittings or the chassis may be damaged. Modular pressure standard stations have threaded connections to the chassis and the threads may become crossed or damage the module, the controller, or both. Fittings can also be damaged if the module is connected with too much torque. In conventional modular systems, data associated with the pressure standard module is stored in a central location in the pressure controller and is lost when one module is swapped for another.
The foregoing problems have generated a need for a more efficient modular pressure controller/calibrator that enables an operator to more quickly connect and disconnect the pressure standard modules with the chassis and a module that prevents damage to the module and the controller and prevents loss of the data associated with each pressure standard module.